Abstract:

Phononic crystal wave structures and methods of making same are discussed
in this application. According to some embodiments, an acoustic structure
can generally comprise a phononic crystal slab configured as a
micro/nano-acoustic wave medium. The phononic crystal slab can define an
exterior surface that bounds an interior volume, and the phononic crystal
slab can be sized and shaped to contain acoustic waves within the
interior volume of the phononic crystal slab. The phononic crystal slab
can comprise at least one defect portion. The defect portion can affect
periodicity characteristics of the phononic crystal slab. The defect
portion can be shaped and arranged to enable confinement and manipulation
of acoustic waves through the defect portion(s) of phononic crystal slab.
Other aspects, features, and embodiments are also claimed and described.

Claims:

1. A micro/nano-mechanical acoustical device, the device comprising:a
phononic crystal slab configured as an micro/nano-acoustical wave medium,
the phononic crystal slab defining an exterior surface that bounds an
interior volume, the phononic crystal slab sized and shape to contain
acoustical waves within the interior volume of the phononic crystal
slab;the phononic crystal slab comprising at least one defect portion
that affects periodicity characteristics of the phononic crystal slab,
the defect portion being shaped and arranged to enable confinement of
acoustical waves through the defect portion of phononic crystal slab.

2. The device of claim 1, wherein the phononic crystal slab has a
thickness ranging from less than a wavelength of the carried acoustical
waves to about ten times the wavelength of the carried acoustical wave.

3. The device of claim 1, further comprising opposing end anchors
respectively located at opposing ends of the phononic crystal slab to
support the phononic crystal slab over a void.

4. The device of claim 1, wherein the defect portion is a linear defect
region centrally disposed along the phononic crystal slab, the linear
defect region ranging from at least one line to a plurality of lines, the
linear defect region being straddled by phononic crystal plate sections
that comprise a periodic array of inclusions.

5. The device of claim 1, wherein the at least one defect portion is
arranged as a two-dimensional defect region disposed at a predetermined
position along the phononic crystal slab.

6. The device of claim 1, wherein the at least one defect portion
comprises at least one of a lack of inclusions, inclusions of different
sizes, inclusions of different locations, and inclusions of different
shapes.

7. The device of claim 1, further comprising a first transducer and a
second transducer, both proximately situated to the phononic crystal
slab, the first transducer providing the acoustical waves and the second
transducer receiving the acoustical waves.

8. The device of claim 1, the phononic crystal slab further comprising at
least one phononic crystal plate section that comprises a
multi-dimensional array of periodic inclusions.

9. The device of claim 1, wherein the phononic crystal slab is a
sub-component of at least one of a mechanical resonator, a waveguide, a
multiplexer, a demultiplexer and a filter.

10. The device of claim 1, wherein the phononic crystal slab is an
unsupported silicon plate and comprises a lattice array of periodic
inclusions.

11. The device of claim 10, wherein the lattice array of periodic
inclusions includes at least one of a triangular lattice, a square
lattice, a hexagonal lattice, or a polygonal lattice.

12. The device of claim 1, wherein the at least one defect portion ranges
from a defect point to a defect region that comprises a plurality of
defect points.

13. In a communications device capable of receiving data from and
transmitting data to another communications device, the communications
device comprising an acoustical wave system enabling acoustical waves to
pass through the system via a micro/nano-mechanical acoustical device,
the acoustical wave system comprising:a phononic crystal acoustic wave
medium disposed between an input transducer and an output transducer, the
acoustical wave medium enabled to allow acoustic waves to propagate
between the transducers, the input transducer configured to excite the
acoustic wave medium and the output transducer configured to receive
acoustical wave excitation energy;the acoustic wave medium comprising a
plurality of phononic crystal plate sections each containing a
multi-dimensional periodic array of inclusions, the periodic array of
inclusions being disposed so that only acoustic waves of predetermined
frequency or range of frequencies to propagate through the acoustic wave
medium;the acoustic wave medium being sized and shaped to contain
acoustical waves within the interior volume space of the acoustic wave
medium; andthe acoustic wave medium comprising at least one defect region
disposed among the periodic array of inclusions, the defect region
capable of allowing acoustic waves to propagate through the defect
region.

14. The acoustical wave system of claim 13, wherein the input and output
transducers are located at least one of proximate the phononic crystal
plate sections, proximate the defect region, and on the at least one
defect region in an integrated fashion.

15. The acoustical wave system of claim 13, wherein the acoustical wave
system forms at least a part of a resonator or filter component in the
communications device.

16. The acoustical wave system of claim 13, wherein the multi-dimensional
periodic array of inclusions are disposed to form a boundary with the at
least one defect region.

17. The acoustical wave system of claim 13, wherein the multi-dimensional
periodic array of inclusions comprise at least one of a series of holes
and dots formed on exterior surface of the acoustic wave medium.

18. The acoustical wave system of claim 13, wherein the at least one
defect region is a linearly-shaped defect region that is disposed
intermediate two multi-dimensional periodic array of inclusions.

19. The acoustical wave system of claim 13, further comprising a first
anchor and a second anchor, the first anchor located proximate to a first
end of the acoustic wave medium and the second anchor located proximate
the second of the acoustic wave medium, the first anchor and the second
anchors situated beneath an exterior surface of the acoustic wave medium
and having approximately equal heights to raise the acoustic wave medium
above a void area defined beneath the acoustic wave medium so that the
acoustic wave medium forms a membrane supported by the anchors, and
wherein the anchors are situated away from the phononic crystal plate
sections.

20. The acoustical wave system of claim 13, wherein the plurality of
phononic crystal plate sections contain at least one of the same
periodicity arrangement, a different periodicity arrangement, and a
heterogeneous structure that comprises various materials.

21. The acoustical wave system of claim 13, wherein the phononic crystal
acoustic wave medium comprises silicon and the multi-dimensional periodic
array of inclusions are configured in an at least one of a triangular
lattice, a square lattice, a hexagonal lattice, or a polygonal lattice.

23. The acoustical wave system of claim 13, wherein the phononic crystal
wave medium is configured to operate in at least one of a low frequency
range of frequencies below about 1 megahartz and in a high frequency
range of frequencies above about 1 megahertz.

24. A micro/nano-mechanical acoustical device, the device comprising:a
slab plate sized and shaped to confine acoustical waves within the
interior volume of the slab plate; the slab plate comprising a phononic
crystal region and a non-periodic region, the phononic crystal region
proximately situated to the non-periodic region and configured to bound
acoustical waves in the non-periodic region, and the non-periodic region
configured to allow the acoustic waves to propagate therethrough.

25. The micro/nano-mechanical acoustical device of claim 24, wherein the
non-periodic region is configured to have a linear shape with opposing
ends stretching to opposing ends of the slab plate and is disposed
intermediate the phononic crystal region.

26. The micro/nano-mechanical acoustical device of claim 24, further
comprising:a first anchor and a second anchor respectively disposed at
opposing ends of the slab plate, the first and second anchors sized and
shape to elevate the slab plate above a void space;a first transducer and
a second transducer, both disposed proximate the slab plate, the first
transducer to provide the acoustic waves to excite the non-periodic
region and the second transducer to receive acoustic wave energy based on
excitation of the non-periodic region; andwherein the phononic crystal
region has multiple lattice periodic arrays that generally bound the
non-periodic region.

27. The micro/nano-mechanical acoustical device of claim 24, wherein the
periodicity of the phononic crystal region is configured to enable the
non-periodic region to resonate at a predetermined frequency or in a
predetermined frequency range.

29. The micro/nano-mechanical acoustical device of claim 24, further
comprising a second slab plate sized and shaped to confine acoustical
waves within the interior volume of the slab, the second slab plate
coupled to the slab plate enabling the slab plate and the second slab
plate to form a multi-stage acoustical wave device.

30. The micro/nano-mechanical acoustical device of claim 24, wherein the
phononic crystal region is configured to have periodicity characteristics
to control frequency of acoustic waves passing through the slab plate and
the non-periodic region.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS & PRIORITY CLAIM

[0001]This application claims priority to and the benefit of United States
Provisional Patent Application No. 61/049,003, filed 30 Apr. 2008, which
is incorporated herein by reference in its entirety as if fully set forth
below.

TECHNICAL FIELD

[0003]Embodiments of the present invention relate generally to phononic
crystal structures and more specifically to phononic crystal,
micro/nano-mechanical and acoustic devices configured to conduct and
entrap mechanical and acoustic energy (e.g., waves) for a variety of
applications as discussed herein.

BACKGROUND

[0004]In the wide market of consumer electronics and the growing market of
sensing devices, there is a demand for high quality factor (Q)
micro/nano-mechanical devices. These devices can be used as building
blocks for a variety of devices such as filters, frequency references,
and mass sensors in such applications as wireless communication and
sensing.

[0005]While serving their purpose, there are several loss mechanisms that
limit the quality factor of conventional micro/nano-mechanical acoustic
devices. In the current conventional designs of micro/nano-mechanical
devices, substrates are not completely isolated from a vibrating medium.
Indeed, the resulting structure includes a vibration medium (or
resonating structure) that is anchored to the substrate. This anchoring
configuration results in a loss or attenuation of mechanical energy due
to the mechanical link. Although attempts have been made to reduce the
loss of mechanical energy through these anchor points, this loss cannot
be eliminated completely through conventional methods.

[0006]What is needed, therefore, are improved micro/nano-mechanical
acoustic devices and associated manufacturing methods capable of
providing high quality devices. It is to the provision of such devices,
systems, and methods that embodiments of the present invention are
directed.

SUMMARY OF EXEMPLARY EMBODIMENTS

[0007]Embodiments of the present invention are generally directed to
phononic crystal wave structures. Phononic crystal wave structure can be
configured for use in a wide variety of applications, including, but not
limited to sensors and electronic devices for radio frequencies (RF) such
as resonators, multiplexers, de-multiplexers, filters, frequency
reference devices, oscillators, delay lines, phase shifters, and
couplers. Numerous of these applications can also be used for wired and
wireless communication systems and sensing systems. Embodiments of the
present invention utilize various properties of phononic crystals (e.g.,
phononic band gaps, small size, and low loss material) to address the
issues discussed above as well as others that conventional devices
posses. Several exemplary embodiments of the present invention are
discussed in this section and additional embodiment and feature details
are discussed throughout this patent application.

[0008]Generally described, embodiments of the present invention include a
micro/nano-mechanical acoustical device. An acoustical device can
generally comprise a phononic crystal slab. The phononic crystal slab can
be configured as an micro/nano-acoustical wave medium. The phononic
crystal slab can define an exterior surface that bounds an interior
volume. The phononic crystal slab can be sized and shape to contain
acoustical waves within the interior volume of the phononic crystal slab.
The phononic crystal slab can comprise at least one defect portion that
affects periodicity characteristics of the phononic crystal slab. The
defect portion can be shaped and arranged to enable confinement of
acoustical waves through the defect portion of phononic crystal slab.

[0009]In other embodiments, the present invention can include an
acoustical wave system for use with wireless communication systems. The
acoustical wave system can generally comprise a phononic crystal acoustic
wave medium. The phononic crystal acoustic wave medium can be disposed
between an input transducer and an output transducer. The acoustical wave
medium can be enabled to allow acoustic waves to propagate between the
transducers. The input transducer can be configured to excite the
acoustic wave medium and the output transducer can be configured to
receive acoustical wave excitation energy. The acoustic wave medium can
comprise a plurality of phononic crystal plate sections, each containing
a multi-dimensional periodic array of inclusions. The periodic array of
inclusions can be disposed so that only acoustic waves of predetermined
frequency or range of frequencies to propagate through the acoustic wave
medium. The acoustic wave medium can be sized and shaped to contain
acoustical waves within the interior volume space of the acoustic wave
medium. Also the acoustic wave medium can comprise at least one defect
region disposed among the periodic array of inclusions. The defect region
can be capable of allowing acoustic waves to propagate through the defect
region.

[0010]Still yet other embodiments are directed to a micro/nano-mechanical
acoustical device. The device can comprise a slab plate sized and shaped
to confine acoustical waves within the interior volume of the slab plate.
The slab plate can comprise a phononic crystal region and a non-periodic
region. The phononic crystal region can be proximately situated to the
non-periodic region and configured to bound acoustical waves in the
non-periodic region, and the non-periodic region configured to allow the
acoustic waves to propagate through the non-periodic region.

[0011]Other aspects and features of embodiments of the present invention
will become apparent to those of ordinary skill in the art, upon
reviewing the following description of specific, exemplary embodiments of
the present invention in conjunction with the accompanying figures. While
features of the present invention may be discussed relative to certain
embodiments and figures, all embodiments of the present invention can
include one or more of the advantageous features discussed herein. In
other words, while one or more embodiments may be discussed as having
certain advantageous features, one or more of such features may also be
used in accordance with the various embodiments of the invention
discussed herein. Also, while exemplary embodiments may be discussed
below as device, system, or method embodiments it should be understood
that such embodiments can be variously implemented in various devices,
systems, and methods.

[0014]FIG. 3 illustrates a general, cross-sectional schematic
representation of an acoustic wave device in accordance with some
embodiments of the present invention.

[0015]FIG. 4 illustrates a perspective view of a general schematic
representation of an acoustic wave device formed with a phononic crystal
structure in accordance with some embodiments of the present invention.

[0016]FIG. 5 illustrates a perspective view of schematic representation of
an exemplary acoustic wave device formed with a phononic crystal
structure and transducers in accordance with some embodiments of the
present invention.

[0017]FIG. 6 illustrates a micrograph image of an acoustic wave device
(top view) formed with a phononic crystal structure in accordance with
some embodiments of the present invention.

[0018]FIG. 7 illustrates another micrograph image of an acoustic wave
device (top view) formed with a phononic crystal structure in accordance
with some embodiments of the present invention.

[0019]FIG. 8 illustrates yet another micrograph image of an acoustic wave
device (top view) formed with a phononic crystal structure in accordance
with some embodiments of the present invention.

[0020]FIG. 9 illustrates a cross-sectional micrograph image of the
acoustic wave device illustrated in FIG. 8 and in particular illustrates
a cross-sectional view of a phononic crystal lattice structure.

[0021]FIGS. 10A-10G (collectively FIG. 10) illustrate various types of
multi-dimensional arrays that can be used to form periodic arrangements
for phononic crystals in accordance with some embodiments of the present
invention.

[0022]FIGS. 11A-11C (collectively FIG. 11) illustrate various schematic
diagrams showing various placements of transducers for use with acoustic
wave devices in accordance with some embodiments of the present
invention.

[0023]FIGS. 12A-12C (collectively FIG. 12) illustrate various schematic
diagrams showing various arrangements formed with multiple acoustic wave
devices in accordance with some embodiments of the present invention.
Also illustrated are possible associated frequency response diagrams
showing frequency response details for the illustrated devices.

[0025]FIG. 14 illustrates a series of frequency response charts depicting
experimental results obtained during testing of acoustic wave devices in
accordance with some embodiments of the present invention.

[0026]FIGS. 15-16 illustrate a frequency response graph illustrating a
phononic band gap of a phononic crystal wave structure in accordance with
some embodiments of the present invention.

[0031]To facilitate an understanding of the principles and features of the
various embodiments of the invention, various illustrative embodiments
are explained below. Embodiments of the present invention are described
below for providing phononic crystal devices and associated fabrication
methods. Embodiments of the invention, however, are not so limited.
Rather, embodiments can include phononic crystal devices with varying
physical characteristics that are capable of providing novel and improved
micro/nano-mechanical acoustic devices.

[0032]Structures with periodic variations in their mechanical properties
are known as phononic crystals (sometimes referred to below as "PnCs").
PnCs have unique frequency characteristics not possible to obtain with
conventional materials. One interesting PnC property is the possibility
of existence of phononic band gaps (PnBGs). PnBGs are frequency bands in
which mechanical energy can not propagate through a structure. PnCs with
PnBGs can be used to filter, confine, or guide mechanical energy and
hence are useful for a variety of applications including, wireless
communications and sensing applications. Planar PnCs with two-dimensional
periodicity can provide a low-loss platform with flexibility in the
fabrication of different lattice types and size and location of periodic
inclusions.

[0033]Exemplary acoustic devices according to some embodiments of the
present invention include a PnC slab. For example in some embodiments,
micro/nano-mechanical devices according to the present invention can be
resonators that include a phononic crystal slab. PnC slabs can comprise a
two dimensional array of inclusions (e.g., holes or raised dots) arranged
across the PnC slab. PnC slabs can also have a limited thickness (e.g.,
on the order of acoustic wavelength). The background environment can be
vacuum, air or any other material. The inclusions can be left empty
(filled by air or remain in vacuum), or filled with another material. The
raised dots can be made of the same material as the slab or a different
material with a thickness that can be smaller or larger than the slab
thickness. By properly choosing the geometrical parameters of the PnC and
the inclusions, it is possible to achieve a phononic band gap (PnBG).

[0034]In some embodiments of the present invention, PnC slab structures
have a small thickness in one dimension and periodicity applied in the
other two dimensions. PnC slab structures can be suspended either in air
or vacuum to decouple the modes in the structure from the modes in the
supporting substrate or mounted on a substrates of a different material.
The PnC slab structure in this case is designed so that the desired
acoustic waves in PnC slab does not propagate in the substrate. As a
result, PnC slab structures can provide a low-loss and flexible platform
to implement functionalities using PnC structures. In currently preferred
embodiments, embodiments of the present invention can be fabricated on a
Silicon substrate. Embodiments of the present invention can, however, be
fabricated with many other materials including, but not limited to, zinc
oxide (ZnO), aluminum nitride (AlN), lead zirconate titanate (PZT),
quartz, lithium niobate (LiNbO3), lithium tantalite (LiTaO3). Embodiments
of the present invention can also be applied to a multi-layer slab
created by stacking several layers of different materials with different
thicknesses on top of each other.

[0035]Referring now to the figures, wherein like reference numerals
represent like parts throughout the views, exemplary embodiments of
phononic crystal devices are described in detail. FIG. 1 illustrates a
schematic diagram of a prior art acoustic wave device (a resonator) 100
that includes anchors disposed between a resonating structure and
opposing substrate components. As shown, the device 100 includes two
substrates 105, 110 and a resonating structure 115 disposed between the
substrates 105, 110. The resonating structure 115 is anchored to the two
substrates 105, 110 via two anchors 120, 125. In operation, the
resonating structure 115 is excited and mechanical energy is received by
a transducer. Due to the resonating structure being anchored to the
substrates 105, 110, however, part of the mechanic energy in the device
is lost to the device substrate. This results in a less than desired Q
factor for the device. Embodiments of the present invention do not
utilize anchors and provide resonating structures with increased Q factor
ratings relative to the device 100.

[0036]FIG. 2 illustrates a schematic representation of a prior art
phononic crystal structure 200 for use with transmitting surface acoustic
waves (SAW). As shown, the structure 200 includes periodic inclusions
proximate a bulk substrate 205 that results in a mechanical energy loss
to the substrate 205. The structure's 200 bulky substrate causes the
mechanical energy loss and this loss results in a Q factor for the
structure that is less than desired. Embodiments of the present invention
aim to address this issue and provide devices with increased Q factor
ratings relative to the structure 200.

[0037]FIG. 3 illustrates a general, cross-sectional schematic
representation of an acoustic wave device 300 in accordance with some
embodiments of the present invention. As shown, the device generally
includes supporting anchors (or supporting pillars) 305, 310 and a
membrane 315 supported by the anchors 305, 310. The anchors 305, 310
support the membrane 315 above a void space or empty region 320. Due to
the acoustic mismatch between the membrane 315 and the void space 320,
there is limited loss of mechanical energy from the membrane 315 to the
void space 320. Thus, the device 300 can provide a low-loss and flexible
platform to implement desired PnC structure functionalities. Void spaces,
such as void space 320, are illustrated in other embodiments shown in the
figures. Sometimes such void spaces may be referred to as voids, void
regions, empty spaces, or free spaces. In some embodiments, the void
space 320 can be filled with one or more other materials. And in some
embodiments, the void space 320 may comprise air or be under vacuum so
that the membrane 315 interfaces with an empty space below the membrane.

[0038]As illustrated, the membrane 315 includes an array of inclusions 325
that give the membrane 315 PnBG characteristics so that only certain
acoustic wave frequencies can propagate through the membrane 315. The
membrane 315 is preferably an acoustic wave medium capable of allowing
acoustic waves to propagate through the membrane 315. According to some
embodiments of the invention, the thickness of the membrane 315 is
limited relative to its length and width. Using a limited thickness
enables acoustic waves to propagate as slab or planar waves through the
membrane 315 while being confined within the membrane 315. The general
arrangement of the device 300 is in general similar to the other
embodiments discussed below so the above details also apply to other
embodiments of the present invention.

[0039]FIG. 4 illustrates a perspective view of a general schematic
representation of an acoustic wave device 400 formed with a phononic
crystal structure in accordance with some embodiments of the present
invention. As shown, the device 400 can include anchors 405, 410 and a
membrane 415. As shown, the thickness of the membrane 415 is limited
relative the length and width of the membrane 415. The membrane 415
includes a PnC portion 420 that includes a periodic multi-dimensional
array of inclusions 425. In the figure, the inclusions 425 are disposed
in a hexagonal lattice array of holes. In other embodiments, the
inclusions 425 may be disposed in other geometrical arrangements and can
be raised surfaces instead of holes.

[0040]The phononic crystal portion 420 can also include other features
according to the present invention. For example, the phononic crystal
portion 420 may include a defect region (or non-periodic portion) that
affects or otherwise disturbs the periodicity of the phononic crystal
portion 420. This can be accomplished by implementing a defect at one or
more points of the periodic lattice. The defect region can be configured
to allow certain acoustic wave frequencies to propagate through the
membrane and also to store mechanical energy. By disposing the phononic
crystal portion 420 at a central portion of the membrane 415, a utilized
defect region can be located intermediate the anchors. In other words, in
a membrane central location, the phononic crystal portion 420 does not
overlay the anchors 405, 410. This arrangement enables a defect region of
the phononic crystal portion 420 to be located away from the anchors.
Advantageously this configuration "uncouples" the energy storing defect
region away from the anchors which aids in providing a desirable quality
factor.

[0041]FIG. 5 illustrates a perspective view of schematic representation of
an acoustic wave device 500 formed with a PnC structure and transducers
in accordance with some embodiments of the present invention. The device
500 can be a PnC slab resonator in accordance with some embodiments. The
device 500 can generally include a membrane 503 coupled to a substrate on
insulator (SOI) wafer 505. The device 500 can also include two opposing
transducers 510, 515 on its opposing two sides 520, 525. One of the two
transducers can be an input transducer to provide energy to excite the
membrane and the other transducer can be an output transducer to receive
mechanical energy from the membrane. As shown, the transducers can be
located on opposing ends of the membrane. In some embodiments, the device
500 can have a width of approximately 1.2 mm while being configured to
transmit acoustic waves having a wavelength of approximately 50 μm. In
other embodiments, the PnC can confine acoustic waves ranging from less
than the thickness of the membrane to approximately ten times the
thickness of the membrane. Still yet, in other embodiments, the phononic
crystal slab can have a thickness ranging from less than a wavelength of
carried acoustical waves to about ten times the wavelength of the carried
acoustical wave.

[0042]The device 500 can also include other features as shown. For
example, the membrane 503 can include multiple phononic crystal
structures 530, 535 and a phononic crystal cavity region 540 disposed
between the phononic crystal structures. In this illustrated embodiment,
the cavity region 540 is surrounded by four rows of holes (one period of
the PnC) on each side. The cavity region 540, also known as a defect
region, can be configured to confine, guide, or hold mechanical
(acoustic) energy transmitted through the device 500.

[0043]FIG. 6 illustrates a micrograph image of an acoustic wave device 600
(top view) formed with a phononic crystal structure in accordance with
some embodiments of the present invention. The device 600 embodiment
shown in FIG. 6 generally includes an input transducer 605, an acoustic
wave medium 610, and an output transducer 615. The acoustic wave medium
610 is preferably configured to allow acoustic waves to propagate as slab
waves through the medium 610. For example, the medium can be configured
as a slab having limited thickness relative to its length and width. As
shown, the medium 610 can have multiple phononic crystal regions 620, 625
and a phononic crystal cavity 630. The phononic crystal cavity 630 can be
a defect region in that affects the periodicity of the phononic crystal
regions. In this embodiment, the phononic crystal cavity 630 is
configured in a linear arrangement. It should be understood, however,
that the phononic crystal cavity 630 can have many different shapes or
arrangements in accordance with embodiments of the present invention.

[0044]FIG. 7 illustrates another micrograph image of an acoustic wave
device 700 (top view) formed with a phononic crystal structure in
accordance with some embodiments of the present invention. The device 700
shown in FIG. 7 is similar to the device 600 shown in FIG. 6. Indeed, the
device 700 generally includes an input transducer 705, an acoustic wave
medium 710, and an output transducer 715. The acoustic wave medium 710 is
preferably configured to allow acoustic waves to propagate as slab waves
through the medium 710. As shown, the medium 710 can have multiple
phononic crystal regions 720, 725 and a phononic crystal cavity 730.

[0045]One difference between the devices shown in FIGS. 6 and 7 is the
configuration of the multiple phononic crystal regions 620, 625, 720,
725. In particular, in the device 700 shown in FIG. 7, the phononic
crystal regions 720, 725 have additional rows of periodic inclusions
relative to the phononic crystal regions 620, 625. Advantageously, by
increasing the number of rows of periodic inclusions, a higher quality
factor for acoustic wave devices can result. Thus according to some
embodiments of the present invention, the Q factor of an acoustic wave
device (e.g., a resonator) is a function of the number of rows of
periodic inclusions provided on an acoustic wave medium. In experiments
between the devices of FIG. 6 and FIG. 7, the inventors found the device
of FIG. 7 had a higher Q factor than that of FIG. 6 due to the additional
number of rows of periodic inclusions. These experiments are discussed
below in more detail with reference to FIG. 14.

[0046]Turning now to FIG. 8, this figure illustrates yet another
micrograph image of an acoustic wave device 800 (top view) formed with a
phononic crystal structure in accordance with some embodiments of the
present invention. The device 800 generally includes an input transducer
805, an acoustic wave medium 810, and an output transducer 815. The
acoustic wave medium 810 is preferably configured to allow acoustic waves
to propagate as slab waves through the medium 810. In this embodiment,
the acoustic wave medium 810 includes a phononic crystal region 820 that
comprises a hexagonal (honeycomb)-lattice structure. FIG. 9 is a
cross-sectional micrograph image the acoustic wave device 800, and this
figures specifically shows a cross-sectional view of the
hexagonal-lattice structure. Also shown in FIG. 9 is a close up view of
electrodes forming part of a transducer (which can either be the input
transducer 805 or the output transducer 815).

[0047]As shown in FIGS. 8-9, the phononic crystal region 820 includes a
multi-dimensional array of holes that form the hexagonal lattice
structure. The multi-dimensional array yields a periodicity in two
dimensions (x and y) as shown in FIG. 8. As shown with reference to FIG.
9, the acoustic wave medium's 810 thickness (or z dimension) is
magnitudes less than the acoustic wave medium's x and y dimensions. In
accordance with some embodiments of the present invention, the ratio
between these magnitudes can range from one to three hundred. It should
be understood, however, that device size and dimensions can be tailored
upon application requirements and/or specifications.

[0048]While the device 800 may be used as an acoustic wave device in some
embodiments, in others, the device 800 can be used to modify the phononic
crystal region 820. For example, in some embodiments, the phononic
crystal region 820 can be modified so that the region includes one or
more defects. This modification can produce a defect region. Modification
can be done on a specific point basis (e.g., filling or removing, change
of size, displacement) in one or more specific holes (or inclusions) in
the phononic crystal region) or on a larger scale bases (e.g., filling
(or removing, change of size or displacement) in multiple holes) to
obtain desired modification results. Modification of the phononic crystal
region 820 can result in any formed defect region to be bounded and/or
surrounded by the phononic crystal region 820. It should be understood,
that while holes are shown in FIGS. 8-9 other types of inclusions (such
as holes filled with other materials or materials put on top of the slab)
may also be used to create the phononic crystal region 820. It should
also be understood that other polygonal geometries (e.g., square-lattice
or triangular lattice) can be used to create the multi-dimensional array
and lattice structure shown in FIGS. 8-9. It should also be understood
that the cross-sectional shape of the inclusions (here circles) can de
designed to retain any desired regular or irregular geometrical shape
(e.g., circle, square, rectangle, triangle).

[0049]FIGS. 10A-10G (collectively FIG. 10) illustrate various types of
multi-dimensional arrays that can be used to form periodic arrangements
for phononic crystals in accordance with some embodiments of the present
invention. FIG. 10A shows an exemplary multi-dimensional array 1005 of
square lattices. Each of the shown squares comprise four holes, and the
center of the holes represents vertex points of where sides of the square
intersect at square corners. FIG. 10B shows a close up view of a
multi-dimensional array 1010 of hexagonal lattices, in which the centers
of each hole represent the intersection of hexagon sides. FIG. 10C
illustrates a close up view of a phononic crystal slab structure 1015
that comprises a plurality of phonic crystal regions 1020, 1025 separated
by a non-periodic region 1030 (or defect region). The phononic crystal
slab regions 1020, 1025 are formed with periodic hexagonal lattices (like
those shown in FIG. 10B). FIG. 10D shows a close up view of a phononic
crystal slab structure 1032 that comprises a plurality of square lattice
structures. Shown in FIG. 10E is an arrangement of dots forming an
exemplary multi-dimensional array 1035 of triangular lattices.

[0050]In some embodiments of the present invention, it may be desired to
use dots (which can be raised surfaces) as opposed to holes. Thus, dots
(or pillars or pillar sections) can be used to provide a periodic
configuration to provide a phononic crystal region in accordance with
some embodiments of the present invention. Choosing between holes or
raised sections may be based partially on device size and/or
manufacturing details.

[0051]FIGS. 10F and 10G show additional embodiments and manners in which
acoustic wave devices of the present invention can be provided. The
acoustic wave medium 1037 in FIG. 10F includes a defect region 1040
disposed intermediate two phononic crystal regions 1045, 1050. As is
shown, the edges of the defect region 1040 are bounded by the two
phononic crystal regions 1045, 1050. In this arrangement, the geometry of
the two phononic crystal regions 1045, 1050 can be chosen so that
mechanical vibrations are confined with the defect region 1040. In some
embodiments, the acoustic wave medium can be used as a waveguide. By
providing the defect region in a linear shape such as the defect region
1040, acoustic waves of a certain frequency can be guided by the defect
region 1040. Due to the PnBG properties of the two phononic crystal
regions 1045, 1050, acoustic waves in a band gap will be prevented from
propagating through the two phononic crystal regions 1045, 1050 and thus
confined within the defect region 1040. To provide a waveguide
embodiment, such as the one shown in FIG. 10F, it may be desired to
utilize phononic crystal regions 1045, 1050 having same periodicity
characteristics. This way, controlling propagating characteristics of
acoustic waves can be accomplished. In other embodiments, it may be
desirable to utilize phononic crystal regions 1045, 1050 having varied
periodicity characteristics.

[0052]In some embodiments, such as the one shown in FIG. 10G, defect
regions can be surrounded or enclosed by phononic crystal structures.
Such a configuration can advantageously confined mechanical energy
vibrations to a specific region in accordance with some embodiments of
the present invention. The acoustic wave medium 1055 in FIG. 10G includes
a defect region 1060 surrounded by different phononic crystal regions
1065, 1070, 1075, 1080. While illustrated as being surrounded by four
different regions, the number of regions can vary according to numerous
embodiments. As is shown, peripheral edges of the defect region 1060 are
surrounded by the phononic crystal regions 1065, 1070, 1075, 1080. In
this arrangement, the geometry of the phononic crystal regions 1065,
1070, 1075, 1080 can be chosen so that mechanical vibrations are confined
with the defect region 1060. The phononic crystal regions 1065, 1070,
1075, 1080 can be configured with the same or different periodic
characteristics which can in turn affect operational characteristics of
the acoustic wave medium 1055 when excited with stimulus.

[0053]As discussed above, use of phononic crystals as acoustic wave
mediums enables the ability to use PnBGs for a variety of applications.
By configuring the geometry of a phononic crystal as desired it is
possible to fabricate a phononic crystal wave structure with
predetermined band gap behavior. The band gap characteristics are
generally a function of inclusion arrangement, inclusion geometry, and
phononic crystal substrate geometry. By varying these physical
characteristics, desired band gap behavior can be realized.

[0054]As one example, consider the multi-dimensional array 1010 comprising
several hexagonal lattices. The dimensional references in FIG. 10B are as
follows: d is the thickness of the PnC slab; α is the distance
between the centers of the nearest holes in the structure; and r is the
radius of the holes. Say these parameters are chosen with the following:
d=15 μm, α=15 μm, and r=6.5 μm. The resulting band
structure of the thin PnC slab (calculated using the known plane wave
expansion method) provides a large PnBG with frequency extent of 115
MHz<f<152 MHz. In other words, by choosing the above dimensions it
is possible to control frequencies at which acoustic waves can not
propagate through the multi-dimensional array of hexagonal lattices. As a
result, such a PnC can be used to confine mechanical vibrations in a wide
frequency range.

[0055]Mechanical energy can be provided to acoustic wave device in various
manners according to embodiments of the present invention. Typically, one
or more transducers can be provided to turn electrical energy into
mechanical energy to excite an acoustic wave medium. For example, FIG. 6
illustrates electrodes disposed on opposing sides of an acoustic wave
medium. As shown, these electrodes are disposed outside of the phonic
crystal range of the acoustic wave medium. One of these electrodes can
excite the acoustic wave medium and the other can received mechanical
energy from the acoustic wave medium in response to the excitation. Other
transducer configurations are also possible with the present invention.

[0056]FIGS. 11A-11C (collectively FIG. 11) illustrate various schematic
diagrams showing various placements of transducers for use with acoustic
wave devices in accordance with some embodiments of the present
invention. In the embodiments shown in FIG. 11, transducer elements can
be disposed in a defect region. In this manner, transducers can supply
and receive mechanical energy directly from a defect region. This feature
enables provision and reception of acoustic waves direct to a defect
region without concern for one or more phononic regions that may bound,
enclose, or surround a defect region. This feature can also enable
obtaining higher quality factor resonators as more PnC inclusions can be
placed around the defect region to achieve stronger acoustic wave
confinement. It also leads to lower device input impedances as the
coupling of the electrical signals to the resonator modes of the
resonator will be more effective in this configuration.

[0057]Now looking at the specifics of FIG. 11, these illustrated
embodiments show additional features of the present invention. For
example, FIG. 11A illustrates an acoustic wave medium 1105 that includes
transducers 1110, 1115 having one or more finger elements 1120a-h for
disposition on a defect region 1115 of the acoustic wave medium 1105. The
finger elements 1105 can be overlapped with each other and arranged in an
alternating fashion as shown. This transducer configuration can be used
to excite a specific mode of the acoustic wave device more efficiently.
FIGS. 11B and 11C show other transducer configurations 1125, 1130 in
which transducers 1135, 1140 are applied directly to defect regions 1145,
1150 (or cavity regions). It should be understood that the transducer
configuration shown in FIG. 11 are just a few alternative transducer
embodiments. Thus, it should be understood that transducer configurations
can vary and in some embodiments be based on resonator mode shape as well
as other operating characteristics.

[0058]The above discussion of acoustic wave devices has for the most part
focused on single-stage devices. But the embodiments of the present
invention are not so limited. Indeed, in accordance with some
embodiments, multi-stage acoustic wave devices can be comprised. In a
general sense, multi-stage acoustic wave devices result from the coupling
of multiple single-stage acoustic wave devices. By coupling multiple
acoustic wave devices together, additional beneficial and operational
characteristics can be obtained. FIGS. 12A-12C (collectively FIG. 12)
illustrate various schematic diagrams showing various devices formed with
multiple acoustic wave devices in accordance with some embodiments of the
present invention. Also illustrated are associated frequency response
diagrams showing frequency response details for the illustrated devices.

[0059]Now turning to the specific details of FIG. 12, FIG. 12A shows
multiple devices coupled together to form a filter 1205, FIG. 12B shows
another filter comprising multiple coupled devices, and FIG. 12C
illustrates a demultiplexer comprising multiple coupled acoustic devices.
As illustrated by the vertical dashed lines, FIG. 12A shows a filter
device that is formed with a series of coupled resonators. A signal with
a variety of frequency components can be cast into the filter, and the
coupled acoustic wave devices will filter the desired frequencies. FIG.
12B shows another filter made from coupled single-stage devices that
filter desired frequencies and produce another filter profile. FIG. 12C
shows a filtering b demultiplexing of signals based on their carrier
frequencies using PnC resonators. As is shown by these figures, acoustic
wave devices according to the present invention (such as PnC resonators)
can be used as building blocks for making filters and demultiplexers. In
some embodiments, only one acoustic wave device may be desired.

[0060]FIGS. 13A-13E (collectively FIG. 13) illustrate schematic images
showing an exemplary logical flow diagram of a method 1300 to fabricate
acoustic wave devices in accordance with some embodiments of the present
invention. It should be understood that the method 1300 is only one
fabrication method and that many others can be implemented in accordance
with the many inventive embodiments. It should further be understood that
more or less process steps can be added or removed from the method 1300
to fabricate a desired acoustic wave device. For example, the method 1300
sets forth a method to fabricate holes for inclusions and other methods
can fabricate dots (or pillars) in an entirely different manner. As
another example, the method 1300 can be tailored to make many different
types of acoustic devices having differing structural or geometrical
characteristics and not just the illustrated acoustic wave device shown
in FIGS. 13A-13E.

[0061]The process 1300 can be initiated by providing a
silicon-on-insulator (SOI) substrate as shown in FIG. 13A. In some
embodiments, the silicon device layer can have a thickness of 15 μm.
Next at FIG. 13B, a thin layer of gold (e.g., ˜100 nm) can be
evaporated and patterned to form electrodes for device transducers. Gold
can be used because it provides an appropriate platform for deposition of
a piezoelectric zinc oxide (ZnO) layer. In a next step as shown in FIG.
13C, a thin (e.g., ˜1 μm) layer of piezoelectric (e.g., ZnO) can
be deposited onto the substrate and patterned using radio frequency (RF)
sputtering and wet etching. Then, a second layer of metal (e.g.,
Aluminum) can be patterned to form a second set of electrodes for the
transducers as shown in FIG. 13D. Next, and as illustrated in FIG. 13 E,
fabrication can continue by patterning and etching PnC holes through the
Si layer. This can be done using optical lithography followed by deep
plasma etching. Finally the lowest substrate and the insulator (e.g., the
oxide) layers can be etched away as shown in FIG. 13E. This etching forms
a PnC membrane and appropriate transducers on the two sides of the
resulting acoustic wave device. All of the various mentioned fabrication
steps are performed at low temperatures, and can be implemented as
post-CMOS processes.

[0062]FIG. 14 illustrates a series of frequency response charts depicting
experimental results obtained during testing of acoustic wave devices in
accordance with some embodiments of the present invention. As mentioned
above, when discussing FIGS. 6 and 7, the inventors conducted studies of
various PnC acoustic wave devices to analyze Q factor changes as a result
of physical structure. The graphs illustrate normalized transmission
through a PnC cavity slab structure for: (a) first, (b) second studied
mode for the structure with three periods (twelve rows) of PnC holes on
each side of the cavity, (c) first , and (d) second studied mode for the
structure with only two periods (eight rows) of PnC holes on each side of
the cavity. The peak frequency (f), quality factor (Q), and insertion
loss (IL) are given in each figure.

[0063]The normalized transmission profiles at frequencies around the
resonance frequencies of these two modes are shown in FIGS. 14(a) and
14(b). As expected, two peaks associated with the two flexural resonant
modes of the cavity appear in the transmission spectrum of the flexural
waves passing through the PnC structure. A peak in the transmission
profile is centered at 126.52 MHz which is in a very good agreement with
the predicted resonance frequency of 126.0 MHz of the first studied mode
found using FEM. The Q of the transmission profile (and hence the first
resonant mode) is 6300 resulting in a frequency by quality factor product
(FQP) of 0.8×1012 Hz which is among the highest FQPs (a common
figure of merit for micromechanical resonators) reported to date for Si
micromechanical resonators operating at atmospheric pressure.

[0064]The measured frequency of the second peak in the transmission is
149.1 MHz, which is again in excellent agreement with the theoretical
value of 149.5 MHz found using FEM. The Q of the second resonant mode is
measured to be 2128, which is nearly one third of that of the first mode.
This is an expected result as the resonance frequency of the second mode
is much closer to the edge of the PnBG compared to the first mode.

[0065]To evaluate the effect of the number of PnC layers on the Q of the
resonant modes of the PnC resonator, we also fabricated the structure
with only two periods (eight layers) of holes on each side of the cavity
and measured the transmission throughout the PnBG with the same procedure
discussed above. The corresponding normalized transmission profiles of
the two studied modes are shown in FIGS. 14(c) and 14(d). As it can be
seen in FIG. 14, the Q of first and second modes are dropped to 1270 and
680 (as compared to 6300 and 2128 for the previous structure). Reducing
the number of PnC layers results in higher coupling of the PnC cavity
modes to propagating modes of the Si slab and consequently much lower Qs
and lower insertion loss.

[0066]FIGS. 15-16 illustrate a frequency response graph illustrating a
phononic band gap of a phononic crystal wave structure in accordance with
some embodiments of the present invention. The frequency response shown
in FIG. 15 represents the frequency response for the phononic crystal
wave structure shown in FIG. 7. As shown, the experimental results show
that the device in FIG. 7 has a phononic band gap between about 126 MHz
to about 149 MHz. The chart shown in FIG. 16 illustrates that the
phononic crystal wave structure shown in FIG. 8 also has a phononic band
gap and serves to prove the concept that phononic crystals provide a
phononic band gap. As shown, the device in FIG. 8 has a phononic band gap
ranging from about 120 MHz to about 150 MHz.

[0067]FIGS. 17-20 illustrate yet additional embodiments of phononic
crystal wave structures in accordance with some embodiments of the
present invention that comprise acoustic wave mediums fabricated with
layers of multiple materials. As shown in these figures, devices can be
fabricated with vibrating mediums that comprise multiple layers of
materials. In addition, these figures show that layered vibrating mediums
can also be configured for use with inclusions that are formed with holes
or pillars. The layers can be of different or similar thickness. The
total thickness of the slab can be less than 10 times the longest
wavelength in each material used in the stack of layers. As illustrated,
a PnC structure can be provided with a layered slab (plate). The layers
can be of different or similar thickness, The total thickness of the slab
is less than 10 times the longest wavelength in each material used in the
stack of layers.

[0068]FIGS. 21-23 show schematic illustrations of additional transducer
configurations applied to defect regions of limited size in accordance
with some embodiments of the present invention. The devices in FIGS.
21-23 are similar to the device in FIG. 11 in that they show multiple
transducer configurations so those similar details are not repeated here.
FIGS. 21-23 are provided to show that defect regions (or non-periodic
regions) can be limited in size. Indeed, defect regions 2120, 2220, 2320
can be provided by only removing or modifying one inclusion to break up
inclusion periodicity characteristics of the phononic crystal 2105, 2205,
2305. Also as shown, transducer electrodes 2110, 2115, 2210, 2215, 2310,
2315 can be shaped to excite a certain mode of the resonator.

[0069]FIG. 24 illustrates a schematic diagram of an acoustic wave
resonator device 2400 configured with raised pillars in accordance with
some embodiments of the present invention. The device 2400 generally
includes a phononic crystal 2405, an array of periodic inclusions 2410,
and a defect region 2415. In this embodiment, the inclusions 2410 are
raised surfaces (e.g., pillars) and the inclusions form a square around
the defect region.

[0070]FIGS. 25A-25B (collectively FIG. 25) illustrate a wave guide
acoustic device structure 2500 (and associated frequency response chart)
in accordance with some embodiments of the present invention. As shown,
the waveguide 2500 includes a linear defect region that can guide
acoustic waves between opposing phononic crystal section and between the
opposing interdigital electrodes/transducers. The associated frequency
chart shows that the waveguide 2500 has a band gap of about 120 MHz to
about 154 MHz. This enables the waveguide 2500 to guide waves between
this frequency range from one end of the waveguide to the other end of
the waveguide.

[0071]The embodiments of the present invention are not limited to the
particular formulations, process steps, and materials disclosed herein as
such formulations, process steps, and materials may vary somewhat.
Moreover, the terminology employed herein is used for the purpose of
describing exemplary embodiments only and the terminology is not intended
to be limiting since the scope of the various embodiments of the present
invention will be limited only by the appended claims and equivalents
thereof.

[0072]Therefore, while embodiments of the invention are described with
reference to exemplary embodiments, those skilled in the art will
understand that variations and modifications can be effected within the
scope of the invention as defined in the appended claims. Accordingly,
the scope of the various embodiments of the present invention should not
be limited to the above discussed embodiments, and should only be defined
by the following claims and all equivalents.